Photosensitive coating composition and the use thereof for protective purposes

Abstract

Uniform protective coatings, particularly solder resist masks, on printed circuit boards can be produced with coating compositions having a viscosity of 200 to 700 m Pas at 25 DEG C. and comprising a solution of a photosensitive, thermally curable, lacquer-forming substance, wherein there is additionally uniformly dispersed 5 to 50% by weight of a finely divided filler.

What we claim is: 
     
       1. A curtain coating composition yielding uniform coatings with good edge covering having a viscosity of 200 to 700 m Pas at 25° C. and comprising a solution of a photosensitive, lacquer-forming substance, wherein the photosensitive substance is a photosensitive epoxide resin having free curable epoxide groups, admixed with a curing agent or admixed with a curing agent and a curing accelerator, which is further characterised in that there are uniformly dispersed in the solution from 5 to 50% by weight, relative to the photosensitive substance, of a finely divided filler, and that the photosensitive substance is additionally thermally curable. 
     
     
       2. A composition according to claim 1, which has a viscosity of between 200 and 500 m Pas. 
     
     
       3. A composition according to claim 1, wherein the photosensitive substance is a photosensitive epoxide resin having chalcone groups and free curable epoxide groups. 
     
     
       4. A composition according to claim 1, wherein the photosensitive substance is an epoxide resin obtained from bis-1,3(4-glycidyloxybenzal)acetone, 2,2-bis(4-hydroxyphenyl)propane and 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane. 
     
     
       5. A composition according to claim 1, which contains an organic solvent. 
     
     
       6. A composition according to claim 5, wherein the organic solvent is selected from the group consisting of alcohols, cyclic ketones, monoalkylated glycols, ethers and carboxylic acid esters, and mixtures of such solvents. 
     
     
       7. A composition according to claim 5, wherein the organic solvent is selected from the group consisting of tetrahydrofurfuryl alcohol, cyclohexanone, methyl glycol, propyleneglycol monomethyl ether, diethylene glycol dimethyl ether, ethyl glycol mono- and diacetate and glycolic acid n-butyl ester, and mixtures of such solvents. 
     
     
       8. A composition according to claim 1, which contains at least 10% by weight of the filler. 
     
     
       9. A composition according to claim 1, which contains from 10 to 36% by weight of the filler. 
     
     
       10. A composition according to claim 1, which contains from 15 to 30% by weight of the filler. 
     
     
       11. A composition according to claim 1, wherein the filler has a mean particle size of from 0.01 to 10 μm. 
     
     
       12. A composition according to claim 1, which contains as filler a micronised filler having a mean particle size of from 0.01 to 1.5 μm. 
     
     
       13. A composition according to claim 1, which contains a filler selected from the group consisting of: finely divided silicon dioxide, micronised talcum, micronised mica, kaolin, aluminium oxide, aluminium hydroxide, calcium silicate, aluminium silicate, magnesium carbonate, calcium carbonate, zirconium silicate, porcelain powder, glass powder, antimony trioxide, titanium dioxide, barium titanate and barium sulfate, and mixtures thereof. 
     
     
       14. A composition according to claim 1, which contains a filler selected from the group consisting of: finely divided silicon dioxide, micronised talcum, aluminium oxide, antimony oxide and kaolin, and mixtures thereof. 
     
     
       15. A composition according to claim 1, which contains at least 10% by weight of micronised talcum, either alone or in admixture with further finely divided fillers. 
     
     
       16. A process for producing protective masks by applying a thin layer of a coating composition as defined in claim 1 to a printed circuit board by the curtain coating method, subsequently drying and irradiating the layer image-wise while the soldered junctions are being left blank, developing the non-irradiated areas of the layer with a solvent and then curing.